It has hitherto been proposed to utilize a rotatable spindle in conjunction with the ram of a vertical boring mill, the spindle being rotatably journaled within the ram so that the device may be used both for boring and drilling operations. Such arrangements have heretofore required separate tool holders depending upon whether the tool is to be mounted on the ram or on the spindle. Since the ram surrounds the spindle, it was necessary for the tool holders to be of different sizes and the tool holder for the ram could not be used to mount tools on the spindle, or vise versa.
It has been suggested that a single tool holder could be utilized provided the spindle is immobilized during a turning operation. However, where this is done, the resultant reaction forces encountered during a boring operation are transmitted to the ram through the spindle bearings with the result that the bearings quickly lose their precision resulting in rapid burnout.
In contrast to the foregoing, the present invention provides a spindle lock-up device which enables the spindle to function as a fixed tool support without transmitting the resultant reaction forces through the precision bearings which support the spindle.